This application is based on and incorporates herein by reference Japanese patent applications No. 2000-130177 filed Apr. 28, 2000, No. 2000-337642 filed Nov. 6, 2000, and No. 2000-394887 filed Dec. 26, 2000.
The present invention generally relates to an apparatus and method capable of compressing image data in a higher image data compression ratio. More specifically, the present invention relates to an image data compressing method and apparatus that compresses image data separately by modifying color.
Resolving of image data is considerably increased in image display technical fields. To display images, frame buffer memories having very large capacities are required, which are a for multi-value data indicative of multiple gradation and also for primary color data constituting a color. In addition, in order to improve data transfer speeds, these frame buffer memories are built in an IC (integrated circuit). However, this technical solution would cause a cost-up problem. On the other hand, in the case that such a method for cutting out lower-grade bits of image data having lower importance degrees is simply employed to reduce a total data amount, image qualities of resultant images would be readily degraded.
It is therefore an object of the present invention to increase an image data compression ratio, while minimizing degradation of image qualities.
According to the present invention, an image data compressing apparatus comprises, a color selecting unit, a data separating unit and a data compressing unit. The color selecting unit selects an arbitrary color from an original image data. The data separating unit separates the image data into modified data and position data. The modified data is produced by modifying or eliminating a color of an image portion from the image data selected by the color selecting unit. The position data indicates a position where the color image portion selected by the color selecting unit is present. The data compressing unit compresses the modified data and the position data separately. This apparatus is particularly useful for ensuring high continuity of data and increasing data compression.
Preferably, the data separating unit separates the image data into position data, remaining data and all-position data, and separates sequentially the position data into position data and an image in an order of predetermined selected colors. The selected colors are located in the position data, and the image is produced by extracting the selected colors. The compressing unit compresses the remaining data, the all-position data and the position data of each of the selected colors separately.
Preferably, a reconstructing unit is provided for reconstructing a color palette prior to a data converting operation by a data converting unit in the data compressing unit in such a manner that indexes of pixels are approximated to be close to each other, and the pixels are continued in a data processing sequence within the image data.